1. Technical Field
The present disclosure relates to electromagnetic valve actuators and engine valve guides for internal combustion engines.
2. Background Art
Significant improvements in engine function can result by replacing conventional camshaft valve actuation with electromagnetic valve actuators that facilitate independent control of each valve decoupled from the crankshaft. This type of actuator, when combined with the engine valve and associated return spring, can be referred to as a “mass oscillator”. The oscillatory motion of opening and closing the valve is primarily attributable to storing and releasing spring energy with control provided by upper and lower electromagnets selectively energized by the engine controller. When the valve is fully closed, the actuator spring is compressed and stores energy with the upper electromagnet energized to hold the armature stationary against the spring force. To open the valve, the upper electromagnet holding force is reduced to allow the release of stored spring energy which moves the armature and associate engine valve toward the open position. Friction losses oppose this motion and may prevent the armature from reaching the full-open position. To complete the valve opening event, the lower electromagnet is energized to attract and hold the armature in the fully open position. To reduce friction and wear, lubricating oil is generally supplied to the actuator and/or valve stem during operation. However, the lubricating oil contributes to viscous friction loss, which opposes valve stem motion and increases exponentially with decreasing operating temperature. At extremely low temperatures, the force of the springs in combination with the force of the electromagnet may be insufficient to overcome the viscous friction losses and the valve may not operate as intended.